Overpopulation of domestic pets
In some countries, there is an overpopulation of pets such as cats, dogs, and exotic animals. In the United States, six to eight million animals are brought to shelters each year, of which an estimated three to four million are subsequently euthanized, including 2.7 million considered healthy and adoptable.
Source: Wikipedia — Overpopulation of domestic pets (CC BY-SA 4.0)